Recent advances in electronic detection based on nanowires (NWs) and nanotubes (NTs) has revolutionized our ability to provide label-free and real-time, yet sensitive and selective detection of a wide range of chemical and biological species using the NW or NT as the gate of a planar field effect transistor (FET). (Cui, Y. et al., Science, 293:1289-1292 (2001)) Unlike two-dimensional FETs, one-dimensional nanowires avoid the reduction in conductance changes caused by lateral current shunting to the point that even single-molecule detection is possible. The selectivity of the nanosensors can be further enhanced by modification with specific bioreceptors such as antibodies. For example, silicon nanowire (SiNWs) functionalized with biotin was used for highly sensitive, real-time and label-free detection of anti-biotin antibody. (Cui, Y. et al., Science, 293:1289-1292 (2001)). Similarly, human autoantigen (UTA) functionalized carbon nanotubes (CNT) were applied for label-free, sensitive and real-time detection of anti-UTA antibody. (Chen, R. J. et al., PNAS, 1000:4984-4989 (2003)) The suggested mechanism for the resulting high sensitivity is the extremely sensitive modulation of the electrical conductance/resistance of the NWs and NTs brought about by the changes in the electrostatic charges from surface adsorption of various molecules. The binding of analytes to the NWs or NTs leads to the depletion or accumulation of carriers in the “bulk” of the nanometer diameter structure and increases the sensitivity to potentially a single molecule.
While these reports demonstrated the power of nanoengineered materials as biosensors, the fabrication methods employed are seriously limited. The techniques of manipulating individual carbon nanotube onto pre-patterned electrodes by an atomic force microscope, (Roschier, L. et al., P., Appl. Phys. Lett., 75:728-730 (1999)) random dispersion of suspended carbon nanotubes onto prepatterned electrodes (Tans, S. J. et al., Nature, 393:49-52 (1998); Bezryadin, A. et al., Phys. Rev. Lett., 80:4036 (1998)) and lithographically patterning catalyst (as carbon nanotube nucleation sites) on electrodes (Franklin, N. R. et al., Appl. Phys. Lett., 81:913-915 (2002); Guillorn, M. A. et al. Appl. Phys. Lett. 81:2860-2862 (2002)), while adequate for demonstrating the operational characteristics of individual devices, have low throughput and limited controllability and hence unattractive for scaling up to high-density sensor arrays. More importantly, surface modifications, typically required to incorporate bioreceptors, have to be performed post-synthesis and post-assembly. Attempts to improve fabrication controllability using either electric field alignment (Smith, P. A. et al., Appl. Phys. Lett., 77:1399-1401 (2000); Duan, X. et al., Nature, 409:66-69 (2001)) or fluidic alignment followed by e-beam lithography have been reported. (Cui, Y. et al., Science, 293:1289-1292 (2001); Huang, Y. et al., Science, 294:1313-1317 (2001)) However, no report to-date has demonstrated the ability to assemble these nanomaterials into a functional sensor circuit and to individually address each nanostructured sensing elements with the desired bioreceptor, a requirement necessary for the successful fabrication of nanosensor arrays.